Air duct systems, especially in commercial and institutional buildings, require dampers at various locations, to restrict flow of fire, smoke and combustion products in the event of a fire. Such dampers are required to operate automatically, in response to various conditions. In the majority of cases they will never be operated at all, since there will be no fire or smoke in the building. However, such dampers must be designed so that they will operate effectively, even after many years of inactivity, during which dust and the like may accumulate. In order to ensure that the dampers are in satisfactory working order, it is customary to test them from time to time. It is clearly desirable for such testing to be carried out from a remote location, without the need for opening up the air duct system at the location of each damper.
Numerous fire damper systems have been proposed in the past which have usually operated on the basis of a powerful spring, and a heat fusible metal link. The link was designed to melt at a certain temperature, thereby permitting the spring to activate the damper and close the duct.
In practice it is found that after a few years or many years of non-use, the blades or other components of the damper become so plugged with dust, etc. that they may, in some cases, have been rendered inoperative. Generally speaking, in these earlier devices. this condition could not be detected from outside the duct. The only way in which such earlier fire dampers could be checked was simply by opening up the duct and releasing the mechanism and cleaning them, and thereafter resetting them.
Even when these devices were in satisfactory working condition, they would operate satisfactorily only under certain restricted conditions, i.e. conditions of high heat. However, they were not sufficiently sensitive to operate effectively to limit the passage of smoke which had not yet reached a temperature high enough to destroy the fusible link. Thus, smoke from a fire in one location might well be transferred throughout a building, causing smoke damage and possible injury or endangering lives, without ever reaching a temperature sufficient to activate the fire dampers.
Clearly, it is desirable to provide a fire damper which is more sensitive, and can respond both to high temperature combustion products, and also to lower temperature smoke. In addition, it is desirable to provide such a fire damper which also permits the mechanism to be operated from a remote location, both in an emergency, and for testing purposes, and which provides visual proof that it is operating satisfactorily, without having to open up the ducts.
One form of damper which goes part way to meeting these objectives is shown in U.S. Letters Pat. No. 4,080,978. For various reasons, however, this is not completely satisfactory, and it is somewhat complex and expensive to manufacture.
One particular disadvantage of more complex fire damper designs is the fact that such fire dampers are, generally speaking, custom made for a particular building. The engineering of the air duct system, requiring different sizes of ducts at different locations, involves the manufacture of fire dampers designed to fit each particular size of duct as used in the building. In many cases in the past, the design of this type of more complex fire damper requiring two different functions, has been such that the assembly of the fire damper was carried out on site by relatively unskilled personnel. A variety of different levers, springs, locks and links were used in different locations on such fire dampers, to provide the multiple different functions. Such complexity has led to components being assembled in the wrong way, in some cases.
The design of the building air system may require that the fire damper be capable of being adjusted during normal operation to a partly closed position, which may be changed at different times, to balance air flows in the system. Preferably, this is achieved by power operated means, such as an electric motor.
It is, however, essential that this shall not interfere with the operation of the damper in an emergency.
It is desirable to provide an actuating mechanism for dampers which is factory built and combines all of the various different functions in one assembly, so that it may be simply attached to the fire damper frame at a predetermined location, thus ensuring that it will function effectively in the case of an emergency. An additional advantage achieved by the use of a separate actuator unit is the fact that it may be located on either side of the fire damper, either upstream or downstream, for maximum effectiveness.
Such actuators can also be combined with power operated means, permitting testing of the damper at intervals, and also permitting adjustment of the damper to balance air flows.
The use of such separately manufactured actuator assemblies also means that they can be mass produced in relatively large production runs, thereby reducing mistakes in assembly.